1. Field
The present invention relates to a display device, and, more particularly, to a display device wherein light emitted from a light source is uniformly diffused, whereby high brightness uniformity can be accomplished even at positions relatively close to the light source, resulting in a reduction in a thickness of the display device.
2. Description of the Related Art
Generally, widely-used display devices can be classified into light-emitting display devices and light-receiving display devices. Light-emitting display devices are self-illuminating, and include, for example, a Cathode Ray Tube (CRT) and Plasma Display Panel (PDP). Light-receiving display devices have no self-illuminating function, and a representative example thereof is a Liquid Crystal Display (LCD).
Such a light-receiving display device has no self-illuminating function, and thus, requires a light source to irradiate light to a display panel provided in the display device to display an image on the display panel.
Light sources are classified, according to an installation position thereof, into direct-light type light sources and edge-light type light sources. A direct-light type light source is provided at the rear side of a display panel to directly irradiate light toward the display panel. An edge-light type light source is provided at a side of a light guide panel such that light emitted from the light source is refracted and diffused along the light guide panel so as to be irradiated toward a display panel. Such an edge-light type light source, in which the light source is provided only at a side of the display panel, may suffer from deterioration of brightness uniformity at the center of the display panel when the display panel has a large size. Therefore, large-scale display devices generally adopt the direct-light type light source.
Even when adopting the direct-light type light source, high brightness uniformity is essential to improve the performance of a display device. Brightness is measured as luminous intensity per apparent unit area. Brightness uniformity is a numerical value representing how uniform brightness-distribution of an entire display panel is when light emitted from a light source is irradiated to the display panel. Brightness uniformity is represented by a value between 0% and 100% with higher values representing more uniform distribution of brightness.
Brightness uniformity is closely related with thickness of a display device. Hereinafter, characteristics of a display device according to a conventional display device will be described, on the basis of a relationship between brightness uniformity and a thickness of the display device, with reference to FIG. 1.
Light sources L1 and L2 are arranged with a predetermined interval therebetween. Although the conventional display device adopts a plurality of cylindrical light sources parallel to one another, for convenience of explanation, only the first light source L1 and the second light source L2 are illustrated. The first light source L1 and the second light source L2 emit respective light beams.
First and second brightness curves R1 and R2 represent brightness of light beams, which are irradiated from the first and second light sources L1 and L2 to a display panel P, respectively. As can be intuitively recognized from the first brightness curve R1 having a convex center C, brightness of a light beam emitted from the first light source L1 is highest at the center C as an upper end of the first brightness curve R1, and decreases gradually away from the center C. It can be understood from the second brightness curve R2, showing a similar pattern to the first brightness curve R1, that the above-described characteristic is similarly observed in the case of the second light source L2.
The first and second brightness curves R1 and R2 of light beams emitted from the first and second light sources L1 and L2 have an overlapping region, and mixing of the light beams occurs at the overlapping region. The mixing of light beams has characteristics of “additive color mixture”. The term “additive color mixture” denotes that light beams overlap each other, yielding a brighter color than their original colors. This phenomenon occurs because the intensity of visually recognizable light beams increases as the light beams are mixed. With the additive color mixture, brightness increases at the overlapping region of the first and second brightness curves R1 and R2. As a result, brightness-distribution represented by a combined brightness curve R3 is obtained.
It can be understood from the combined brightness curve R3 that a constant brightness area F, which has brightness similar to the highest brightness of the center C, occurs between the first light source L1 and the second light source L2. As described above, if several light sources are arranged with an appropriate interval in addition to the first and second light sources L1 and L2, the constant brightness area F is continuously extended, whereby the several light sources have the effect of a single surface light source. Accordingly, when a display panel P is located at a position distant from the ground surface B by a first distance D1, the entire display panel P can achieve uniform brightness.
However, due to the fact that the display panel P should be located in the constant brightness area F, the conventional display device requires an interior space distant from the ground surface B by at least the first distance D1, and consequently, is problematically thick.
The above-described problem is further clearly recognized from the fact that a display panel P exhibits uneven brightness when it is distant from the ground surface B by a shorter second distance D2 in order to reduce a thickness thereof.